The present invention relates to a polyurethane matrix-containing gel composition and a process for the production thereof. This gel composition may include active ingredients which ingredients may be released from the matrix to the surrounding environment. This gel composition may be used in making impressions for molding.
Gel compositions are known to those in the art. Such compositions have been used as support media for active ingredients which ingredients are given off to the surrounding environment over a period of weeks or even months. (See e.g. U.S. Pat. Nos. 3,822,238 and 3,975,350). Polyurethane polyurea gels containing water and/or alcohol which perfumed substances have been incorporated have also been prepared. For example, German Offenlegungsschrift No. 2,521,265 describes use of aqueous gels as carriers for a wide variety of materials such as pharmaceuticals, biocidal agents and perfumes. However, the known aqueous gels have the disadvantage that many agents (particularly biocidal agents) are subject to fairly rapid decomposition in the presence of water so that the length of time during which gels containing these agents are active is greatly reduced.
It is also known to incorporate active substances into solid and/or foamed high molecular weight polyurethanes (e.g. Swiss Pat. No. 289,915) but such high molecular weight polyurethanes are disadvantageous in that a high proportion of the liquid agents incorporated therein remain in the polyurethane (due to the molecular structure) and can not therefore be given off to the surrounding environment. Further, solid active ingredients may be used in such foamed polyurethanes only to a very limited extent. Active ingredients which are not volatile do not migrate out of the polyurethane mass whereas those solid agents that are highly volatile may only diffuse out of the foam for a very short period of time and in very small quantities.
Aqueous gels have been used in many other industrial applications (See e.g. R. L. Whistler, Industrial Gums, Academic Press, Inc., NY, 1973 and DE-AS (German Published Specification) No. 2,347,299. Because of their capability for a high degree of accuracy in making impressions, these gels have been found to be particularly useful in replicating molded articles. In such replication processes, the gel-forming composition is poured over the object of which an impression is to be taken. After formation of the gel, the article is removed from the gel-mold which mold is a cavity corresponding in volume to that of the original article. Such molds have many applications. In the field of denistry, for example, agar-agar gel is frequently used as a replicating composition. These aqueous compositions are, however, disadvantageous in that: (1) gellation requires a long period of time and must be carried out under specific process conditions; (2) elasticity of the gel is not high enough to permit removal of thin projections and undercuts from the mold; and (3) dimensional stability is poor (as can be seen from the fact that on open storage of the gel mold, a change in the proportions of the mold occurs after a brief period of time) due to water evaporation.
Anhydrous compositions useful in making mold impressions are also known. Such compositions may be based, for example, on silicones. These compositions may be prepared by mixing a pre-polymer with a small amount of a cross-linking agent. This mixture is then poured over the object of which an impression is to be taken. The original object is removed after the mold composition has hardened leaving a mold with a cavity in which casts of the original articles may be produced. These anhydrous compositions are, however, disadvantageous in that: (1) the viscosity of the mold composition is too high to form accurate impressions of objects having fine indentations and undercuts in the surface; and (2) the reaction time is much too long. Attempts to shorten the reaction time by increasing the proportion of cross-linking agent results in a significant degree of mold shrinkage.